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BACKGROUND: Virtual reality and interactive video gaming have emerged as recent treatment approaches in stroke rehabilitation with commercial gaming consoles in particular, being rapidly adopted in clinical settings. This is an update of a Cochrane Review published first in 2011 and then again in 2015. OBJECTIVES: Primary objective: to determine the efficacy of virtual reality compared with an alternative intervention or no intervention on upper limb function and activity.Secondary objectives: to determine the efficacy of virtual reality compared with an alternative intervention or no intervention on: gait and balance, global motor function, cognitive function, activity limitation, participation restriction, quality of life, and adverse events. SEARCH METHODS: We searched the Cochrane Stroke Group Trials Register (April 2017), CENTRAL, MEDLINE, Embase, and seven additional databases. We also searched trials registries and reference lists. SELECTION CRITERIA: Randomised and quasi-randomised trials of virtual reality ("an advanced form of human-computer interface that allows the user to 'interact' with and become 'immersed' in a computer-generated environment in a naturalistic fashion") in adults after stroke. The primary outcome of interest was upper limb function and activity. Secondary outcomes included gait and balance and global motor function. DATA COLLECTION AND ANALYSIS: Two review authors independently selected trials based on pre-defined inclusion criteria, extracted data, and assessed risk of bias. A third review author moderated disagreements when required. The review authors contacted investigators to obtain missing information. MAIN RESULTS: We included 72 trials that involved 2470 participants. This review includes 35 new studies in addition to the studies included in the previous version of this review. Study sample sizes were generally small and interventions varied in terms of both the goals of treatment and the virtual reality devices used. The risk of bias present in many studies was unclear due to poor reporting. Thus, while there are a large number of randomised controlled trials, the evidence remains mostly low quality when rated using the GRADE system. Control groups usually received no intervention or therapy based on a standard-care approach. PRIMARY OUTCOME: results were not statistically significant for upper limb function (standardised mean difference (SMD) 0.07, 95% confidence intervals (CI) -0.05 to 0.20, 22 studies, 1038 participants, low-quality evidence) when comparing virtual reality to conventional therapy. However, when virtual reality was used in addition to usual care (providing a higher dose of therapy for those in the intervention group) there was a statistically significant difference between groups (SMD 0.49, 0.21 to 0.77, 10 studies, 210 participants, low-quality evidence). SECONDARY OUTCOMES: when compared to conventional therapy approaches there were no statistically significant effects for gait speed or balance. Results were statistically significant for the activities of daily living (ADL) outcome (SMD 0.25, 95% CI 0.06 to 0.43, 10 studies, 466 participants, moderate-quality evidence); however, we were unable to pool results for cognitive function, participation restriction, or quality of life. Twenty-three studies reported that they monitored for adverse events; across these studies there were few adverse events and those reported were relatively mild. AUTHORS' CONCLUSIONS: We found evidence that the use of virtual reality and interactive video gaming was not more beneficial than conventional therapy approaches in improving upper limb function. Virtual reality may be beneficial in improving upper limb function and activities of daily living function when used as an adjunct to usual care (to increase overall therapy time). There was insufficient evidence to reach conclusions about the effect of virtual reality and interactive video gaming on gait speed, balance, participation, or quality of life. This review found that time since onset of stroke, severity of impairment, and the type of device (commercial or customised) were not strong influencers of outcome. There was a trend suggesting that higher dose (more than 15 hours of total intervention) was preferable as were customised virtual reality programs; however, these findings were not statistically significant.

BACKGROUND: We evaluated the performance characteristics of computed tomographic (CT) virtual colonoscopy for the detection of colorectal neoplasia in an average-risk screening population. METHODS: A total of 1233 asymptomatic adults (mean age, 57.8 years) underwent same-day virtual and optical colonoscopy. Radiologists used the three-dimensional endoluminal display for the initial detection of polyps on CT virtual colonoscopy. For the initial examination of each colonic segment, the colonoscopists were unaware of the findings on virtual colonoscopy, which were revealed to them before any subsequent reexamination. The sensitivity and specificity of virtual colonoscopy and the sensitivity of optical colonoscopy were calculated with the use of the findings of the final, unblinded optical colonoscopy as the reference standard. RESULTS: The sensitivity of virtual colonoscopy for adenomatous polyps was 93.8 percent for polyps at least 10 mm in diameter, 93.9 percent for polyps at least 8 mm in diameter, and 88.7 percent for polyps at least 6 mm in diameter. The sensitivity of optical colonoscopy for adenomatous polyps was 87.5 percent, 91.5 percent, and 92.3 percent for the three sizes of polyps, respectively. The specificity of virtual colonoscopy for adenomatous polyps was 96.0 percent for polyps at least 10 mm in diameter, 92.2 percent for polyps at least 8 mm in diameter, and 79.6 percent for polyps at least 6 mm in diameter. Two polyps were malignant; both were detected on virtual colonoscopy, and one of them was missed on optical colonoscopy before the results on virtual colonoscopy were revealed. CONCLUSIONS: CT virtual colonoscopy with the use of a three-dimensional approach is an accurate screening method for the detection of colorectal neoplasia in asymptomatic average-risk adults and compares favorably with optical colonoscopy in terms of the detection of clinically relevant lesions.

This paper describes a study to assess the influence of a variety of factors on reported level of presence in immersive virtual environments. It introduces the idea of “stacking depth,” that is, where a participant can simulate the process of entering the virtual environment while already in such an environment, which can be repeated to several levels of depth. An experimental study including 24 subjects was carried out. Half of the subjects were transported between environments by using virtual head-mounted displays, and the other half by going through doors. Three other binary factors were whether or not gravity operated, whether or not the subject experienced a virtual precipice, and whether or not the subject was followed around by a virtual actor. Visual, auditory, and kinesthetic representation systems and egocentric/exocentric perceptual positions were assessed by a preexperiment questionnaire. Presence was assessed by the subjects as their sense of “being there,” the extent to which they experienced the virtual environments as more the presenting reality than the real world in which the experiment was taking place, and the extent to which the subject experienced the virtual environments as places visited rather than images seen. A logistic regression analysis revealed that subjective reporting of presence was significantly positively associated with visual and kinesthetic representation systems, and negatively with the auditory system. This was not surprising since the virtual reality system used was primarily visual. The analysis also showed a significant and positive association with stacking level depth for those who were transported between environments by using the virtual HMD, and a negative association for those who were transported through doors. Finally, four of the subjects moved their real left arm to match movement of the left arm of the virtual body displayed by the system. These four scored significantly higher on the kinesthetic representation system than the remainder of the subjects.

Virtualization is a hot topic in operating systems these days. It is useful in many scenarios: server consolida-tion, virtual test environments, and for Linux enthusiasts who still can not decide which distribution is best. Re-cently, hardware vendors of commodity x86 processors have added virtualization extensions to the instruction set that can be utilized to write relatively simple virtual machine monitors. The Kernel-based Virtual Machine, or kvm, is a new Linux subsystem which leverages these virtualization extensions to add a virtual machine monitor (or hyper-visor) capability to Linux. Using kvm, one can create and run multiple virtual machines. These virtual ma-chines appear as normal Linux processes and integrate seamlessly with the rest of the system. 1

Network virtualization is a powerful way to run multiple architectures or experiments simultaneously on a shared infrastructure. However, making efficient use of the underlying resources requires effective techniques for virtual network embedding--mapping each virtual network to specific nodes and links in the substrate network. Since the general embedding problem is computationally intractable, past research restricted the problem space to allow efficient solutions, or focused on designing heuristic algorithms. In this paper, we advocate a different approach: rethinking the design of the substrate network to enable simpler embedding algorithms and more efficient use of resources, without restricting the problem space. In particular, we simplify virtual link embedding by: i) allowing the substrate network to split a virtual link over multiple substrate paths and ii) employing path migration to periodically re-optimize the utilization of the substrate network. We also explore node-mapping algorithms that are customized to common classes of virtual-network topologies. Our simulation experiments show that path splitting, path migration,and customized embedding algorithms enable a substrate network to satisfy a much larger mix of virtual networks

As the nature of work in today’s organizations becomes more complex, dynamic, and global, there has been increasing emphasis on distributed, “virtual” teams as organizing units of work. Despite their growing prevalence, relatively little is known about this new form of work unit. The purpose of this article is to present a theoretical framework to focus research toward understanding virtual teams and identifying implications for effective leadership. The authors focus on delineating the dimensions of a typology to characterize different types of virtual teams. First, the authors distinguish virtual teams from conventional teams to identify where current knowledge applies and new research needs exist. Second, the authors distinguish among different types of virtual teams, considering the critical role of task complexity in determining the underlying characteristics of virtual teams and leadership challenges the different types entail. Propositions addressing leadership implications for the effective management of virtual teams are proposed and discussed.

Numerous systems have been designed which use virtualization to subdivide the ample resources of a modern computer. Some require specialized hardware, or cannot support commodity operating systems. Some target 100% binary compatibility at the expense of performance. Others sacrifice security or functionality for speed. Few offer resource isolation or performance guarantees; most provide only best-effort provisioning, risking denial of service.This paper presents Xen, an x86 virtual machine monitor which allows multiple commodity operating systems to share conventional hardware in a safe and resource managed fashion, but without sacrificing either performance or functionality. This is achieved by providing an idealized virtual machine abstraction to which operating systems such as Linux, BSD and Windows XP, can be ported with minimal effort.Our design is targeted at hosting up to 100 virtual machine instances simultaneously on a modern server. The virtualization approach taken by Xen is extremely efficient: we allow operating systems such as Linux and Windows XP to be hosted simultaneously for a negligible performance overhead --- at most a few percent compared with the unvirtualized case. We considerably outperform competing commercial and freely available solutions in a range of microbenchmarks and system-wide tests.

Global virtual teams are internationally distributed groups of people with an organizational mandate to make or implement decisions with international components and implications. They are typically assigned tasks that are strategically important and highly complex. They rarely meet in person, conducting almost all of their interaction and decision making using communications technology. Although they play an increasingly important role in multinational organizations, little systematic is known about their dynamics or effectiveness. This study built a grounded theory of global virtual team processes and performance over time. We built a template based on Adaptive Structuration Theory (DeSanctis and Poole 1994) to guide our research, and we conducted a case study, observing three global virtual teams over a period of 21 months. Data were gathered using multiple methods, and qualitative methods were used to analyze them and generate a theory of global virtual team dynamics and effectiveness. First, we propose that effective global virtual team interaction comprises a series of communication incidents, each configured by aspects of the team's structural and process elements. Effective outcomes were associated with a fit among an interaction incident's form, decision process, and complexity. Second, effective global virtual teams sequence these incidents to generate a deep rhythm of regular face-to-face incidents interspersed with less intensive, shorter incidents using various media. These two insights are discussed with respect to other literature and are elaborated upon in several propositions. Implications for research and practice are also outlined.

Information technology is providing the infrastructure necessary to support the development of new organizational forms. Virtual teams represent one such organizational form, one that could revolutionize the workplace and provide organizations with unprecedented levels of flexibility and responsiveness. As the technological infrastructure necessary to support virtual teams is now readily available, further research on the range of issues surrounding virtual teams is required if we are to learn how to manage them effectively. While the findings of team research in the traditional environment may provide useful pointers, the idiosyncratic structural and contextual issues surrounding virtual teams call for specific research attention.This article provides a review of previously published work and reports on the findings from early virtual team research in an effort to take stock of the current state of the art. The review is organized around the input - process - output model and categorizes the literature into issues pertaining to inputs, socio-emotional processes, task processes, and outputs. Building on this review we critically evaluate virtual team research and develop research questions that can guide future inquiry in this fertile are of inquiry.

Network throughput can be increased by dividing the buffer storage associated with each network channel into several virtual channels. Each physical channel is associated with several small queues, virtual channels, rather than a single deep queue. The virtual channels associated with one physical channel are allocated independently but compete with each other for physical bandwidth. Virtual channels decouple buffer resources from transmission resources. This decoupling allows active messages to pass blocked messages using network bandwidth that would otherwise be left idle. The paper studies the performance of networks using virtual channels using both analysis and simulation. These studies show that virtual channels increase network throughput, by a factor of four for 10-stage networks, and reduce the dependence of throughput on the depth of the network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We propose a new regularization method based on virtual adversarial loss: a new measure of local smoothness of the conditional label distribution given input. Virtual adversarial loss is defined as the robustness of the conditional label distribution around each input data point against local perturbation. Unlike adversarial training, our method defines the adversarial direction without label information and is hence applicable to semi-supervised learning. Because the directions in which we smooth the model are only "virtually" adversarial, we call our method virtual adversarial training (VAT). The computational cost of VAT is relatively low. For neural networks, the approximated gradient of virtual adversarial loss can be computed with no more than two pairs of forward- and back-propagations. In our experiments, we applied VAT to supervised and semi-supervised learning tasks on multiple benchmark datasets. With a simple enhancement of the algorithm based on the entropy minimization principle, our VAT achieves state-of-the-art performance for semi-supervised learning tasks on SVHN and CIFAR-10.

February 01 1992 Musings on Telepresence and Virtual Presence Thomas B. Sheridan Thomas B. Sheridan Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. Search for other works by this author on: This Site Google Scholar Author and Article Information Thomas B. Sheridan Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. © 1992 Massachusetts Institute of Technology1992 Presence: Teleoperators and Virtual Environments (1992) 1 (1): 120–126. https://doi.org/10.1162/pres.1992.1.1.120 Connected Content A correction has been published: Errata Cite Icon Cite Permissions Share Icon Share Facebook Twitter LinkedIn MailTo Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Search Site Citation Thomas B. Sheridan; Musings on Telepresence and Virtual Presence. Presence: Teleoperators and Virtual Environments 1992; 1 (1): 120–126. doi: https://doi.org/10.1162/pres.1992.1.1.120 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsPRESENCE: Virtual and Augmented Reality Search Advanced Search This content is only available as a PDF. © 1992 Massachusetts Institute of Technology1992 Article PDF first page preview Close Modal You do not currently have access to this content.

Although the body has been the focus of much contemporary cultural theory, the models that are typically applied neglect the most salient characteristics of embodied existence—movement, affect, and sensation—in favor of concepts derived from linguistic theory. In Parables for the Virtual Brian Massumi views the body and media such as television, film, and the Internet, as cultural formations that operate on multiple registers of sensation beyond the reach of the reading techniques founded on the standard rhetorical and semiotic models. Renewing and assessing William James’s radical empiricism and Henri Bergson’s philosophy of perception through the filter of the post-war French philosophy of Deleuze, Guattari, and Foucault, Massumi links a cultural logic of variation to questions of movement, affect, and sensation. If such concepts are as fundamental as signs and significations, he argues, then a new set of theoretical issues appear, and with them potential new paths for the wedding of scientific and cultural theory. Replacing the traditional opposition of literal and figural with new distinctions between stasis and motion and between actual and virtual, Parables for the Virtual tackles related theoretical issues by applying them to cultural mediums as diverse as architecture, body art, the digital art of Stelarc, and Ronald Reagan’s acting career. The result is an intriguing combination of cultural theory, science, and philosophy that asserts itself in a crystalline and multi-faceted argument. Parables for the Virtual will interest students and scholars of continental and Anglo-American philosophy, cultural studies, cognitive science, electronic art, digital culture, and chaos theory, as well as those concerned with the “science wars” and the relation between the humanities and the sciences in general.

This paper explores the challenges of creating and maintaining trust in a global virtual team whose members transcend time, space, and culture. The challenges are highlighted by integrating recent literature on work teams, computer-mediated communication groups, cross-cultural communication, and interpersonal and organizational trust. To explore these challenges empirically, we report on a series of descriptive case studies on global virtual teams whose members were separated by location and culture, were challenged by a common collaborative project, and for whom the only economically and practically viable communication medium was asynchronous and synchronous computer-mediated communication. The results suggest that global virtual teams may experience a form of “swift” trust, but such trust appears to be very fragile and temporal. The study raises a number of issues to be explored and debated by future research. Pragmatically, the study describes communication behaviors that might facilitate trust in global virtual teams.

What does it feel like to own, to control, and to be inside a body? The multidimensional nature of this experience together with the continuous presence of one's biological body, render both theoretical and experimental approaches problematic. Nevertheless, exploitation of immersive virtual reality has allowed a reframing of this question to whether it is possible to experience the same sensations towards a virtual body inside an immersive virtual environment as toward the biological body, and if so, to what extent. The current paper addresses these issues by referring to the Sense of Embodiment (SoE). Due to the conceptual confusion around this sense, we provide a working definition which states that SoE consists of three subcomponents: the sense of self-location, the sense of agency, and the sense of body ownership. Under this proposed structure, measures and experimental manipulations reported in the literature are reviewed and related challenges are outlined. Finally, future experimental studies are proposed to overcome those challenges, toward deepening the concept of SoE and enhancing it in virtual applications.

There is growing evidence of the increasing participation in, and influence of, virtual communities in digital environments. To help explain this irresistible allure, the individual and social determinants of the member's intentions to participate are investigated. Conceptualizing virtual community participation as intentional social action, we explicate the concept of “we-intentions”, and use the Model of Goal-Directed Behavior to explain members’ we-intentions. Virtual community influences pertaining to compliance, internalization, and social identity are also elaborated on. An empirical study of regular virtual community participants ( N = 157) finds that we-intentions to participate are functions of both individual determinants (positive anticipated emotions and desires), and community influences (social identity). Implications for marketing and future research opportunities are discussed.

&lt;p&gt;Cyberculture authority Howard Rheingold was the first to write about online communities in this style that is part-travelogue and part-anthropological guide. This groundbreaking classic explores the entire virtual community, beginning with a selective but probing look at the author's original online home, The Well. Rheingold relates plenty of anecdotes that demonstrate the upsides of online life, such as how he was able to get information on removing a tick from his child before his doctor could respond to his phone call. But the bulk of the material relates to how individuals interact online much as they do in a face-to-face community. Rheingold speaks to how both friendships and enmities are formed online and how people come together to support each other through misfortune. He gives the example of how computer-moderated communication enabled members of one Well community to send vital medical aid to a friend hospitalized halfway around the world. Rheingold goes on to show how communities can form by various electronic communication methods, using the conferencing system of The Well as one example. He also examines how people interact through mailing lists, live chat, and the fantasy cyberenvironments of online role-playing games. In the process, he questions what kind of relationships can really be formed in a medium where people can change their apparent identity at will. This book questions whether a distinction between “virtual” communities and “real-life” communities is entirely valid. The Virtual Community argues that real relationships happen and real communities develop when people communicate upon virtual common ground. Rheingold also shares his far-reaching knowledge of how technology effects our social constructs. If you are involved in an online community, here is your cultural heritage. &lt;/p&gt;

In this paper, I address the question as to why participants tend to respond realistically to situations and events portrayed within an immersive virtual reality system. The idea is put forward, based on the experience of a large number of experimental studies, that there are two orthogonal components that contribute to this realistic response. The first is 'being there', often called 'presence', the qualia of having a sensation of being in a real place. We call this place illusion (PI). Second, plausibility illusion (Psi) refers to the illusion that the scenario being depicted is actually occurring. In the case of both PI and Psi the participant knows for sure that they are not 'there' and that the events are not occurring. PI is constrained by the sensorimotor contingencies afforded by the virtual reality system. Psi is determined by the extent to which the system can produce events that directly relate to the participant, the overall credibility of the scenario being depicted in comparison with expectations. We argue that when both PI and Psi occur, participants will respond realistically to the virtual reality.

Virtual time is a new paradigm for organizing and synchronizing distributed systems which can be applied to such problems as distributed discrete event simulation and distributed database concurrency control. Virtual time provides a flexible abstraction of real time in much the same way that virtual memory provides an abstraction of real memory. It is implemented using the Time Warp mechanism, a synchronization protocol distinguished by its reliance on lookahead-rollback, and by its implementation of rollback via antimessages.